Floating in Copper

Explore the slowing effect of eddy currents with your own fingers as you levitate as strong magnet between two pieces of copper.

Explanation

When a magnet is moved near a conductor such as the copper slabs, small rings of electrical current form in the metal. Those rings of electricity are called eddy currents.

Magnetic fields surround eddy currents and repel any magnets that come near them. This causes the magnet to slow down as it moves toward the upper magnet, creating the ‘floating’ appearance.

This slowing effect is used in eddy current braking systems. These systems have the advantage that they don’t wear out as do friction brakes.

Extras for experts

The braking effect is proportional to the speed of the conductor’s movement relative to the magnet. A fast spinning wheel experiences a stronger braking effect compared to a more slowly spinning wheel. This means that a vehicle’s braking speed is smoothed as it slows down to a stop.

Eddy current braking is quite an inefficient process, as it converts kinetic energy to heat energy.

Things to Try

Try floating the magnet from one end of the copper to the other.
How quickly can you make the lower magnet move by dragging the upper magnet along the copper?

When Using This Exhibit

This exhibit contains a strong magnet! Please keep credit cards or any devices that might be affected by magnets, away from this exhibit.
Make sure the lower magnet is sitting horizontally between the copper slabs before you try floating it.

Questions to Ask

Have you ever been on a roller coaster? How do you think it stopped at the end of the ride? Can you think of any problems that might occur if the roller coasters used friction brakes? How do you think you could use magnets as brakes?

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